Info re posts.

As yet, I have not found how to do this in threads I have started, by attempting to edit my first post (#1) or making a reply using the 'Go Advanced' button, I can't mark it as 'Solved'
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If I use the 'Thread Tools' link and select 'Mark this thread as solved' as in my image, the thread gets marked as 'Closed Thread'

Neither. Historically we've just left them open. The reason being that even after some time there could be another better contribution. Automatic closure has been discussed before and rejected for the prior statement. If posts by spammers on old threads become more than we are willing to try to manage then I suspect automatic closure will be revisited.

We added "Solved" as a result of Loungers requests. If a Lounger chooses not to use "Solved" that is OK.